CN116155329A - User clustering and power distribution method of mMIMO-NOMA system based on meta-heuristic algorithm - Google Patents
User clustering and power distribution method of mMIMO-NOMA system based on meta-heuristic algorithm Download PDFInfo
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Abstract
The invention discloses a user clustering and power distribution method of an mMIMO-NOMA system based on a meta-heuristic algorithm, which comprises the following steps: firstly, constructing a millimeter wave mMIMO-NOMA system and constructing a millimeter wave channel model; step two, clustering all users by adopting a user clustering algorithm based on cluster head selection to obtain a user clustering result; step three, mixed pre-coding is carried out aiming at the obtained cluster head channels, and user interference among clusters is eliminated; and fourthly, performing power distribution by using a meta-heuristic algorithm based on fusion PSO-SCSO, and improving the frequency spectrum efficiency and the energy efficiency of the system. The invention is suitable for the multi-user millimeter wave mMIMO-NOMA system, and can effectively improve the frequency spectrum efficiency and the energy efficiency of the system.
Description
Technical Field
The invention belongs to the technical field of millimeter wave communication, and particularly relates to a user clustering and power distribution method of an mMIMO-NOMA system based on a meta-heuristic algorithm.
Background
Currently, wireless communication systems are mainly based on an orthogonal multiple access method, in which spectrum efficiency is low and the number of user accesses is limited. Millimeter wave technology can provide richer spectrum resources; the large-scale multiple input multiple output (massive multiple input multiple output, mMIMO) technology can improve the frequency spectrum efficiency by utilizing space division multiplexing and can compensate the path loss of millimeter waves; the non-orthogonal multiple access (non-orthogonal multiple access, NOMA) technology realizes power domain multiplexing through a serial interference cancellation technology, so that a plurality of users share the same time-frequency resource, and the number of simultaneous connections of the system can be effectively improved. Therefore, millimeter wave MIMO and NOMA are combined, namely a millimeter wave mMIMO-NOMA system, the mixed multiple access of SDMA and NOMA is realized by utilizing an antenna array of MIMO in a clustering mode, the limit of the number of radio frequency chains on the number of user connections can be broken through, and the system is expected to provide data transmission with higher speed and lower power consumption for future wireless networks.
In an mMIMO-NOMA communication system, as the number of users increases, the interference among users can obviously influence the system performance, the interference among different clusters can be solved by a hybrid precoding technology, and the interference among users in the clusters needs to be solved by a reasonable user clustering and power distribution algorithm. In recent years, domestic and foreign scholars have made a great deal of researches on hybrid precoding, user clustering and power distribution, wherein more researches are concentrated on hybrid precoding, more scholars have researched user clustering and power distribution, and various schemes are provided, but the existing power distribution problem is mainly solved by a convex optimization method, the calculation complexity is high, and the traditional machine learning-based user clustering algorithm also needs more complex calculation; in recent years, scholars have proposed using a meta-heuristic algorithm to solve the problem of power allocation of a NOMA system, but in a mMIMO-NOMA system, the number of users increases, and the performance decreases due to defects existing in the traditional meta-heuristic algorithm, so that the design of an efficient user clustering and power allocation algorithm for the mMIMO-NOMA system has important significance.
Disclosure of Invention
The invention provides a user clustering and power distribution method of an mMIMO-NOMA system based on a meta-heuristic algorithm aiming at solving the complex problem of user clustering and power distribution in the mMIMO-NOMA system, and particularly comprises an improved user clustering algorithm based on cluster head selection and an improved meta-heuristic algorithm of fusion particle swarm algorithm (particle swarm optimization, PSO) and a sand cat algorithm (Sand Cat Swarm Optimization, SCSO) for a power distribution scheme, aiming at reducing the calculation complexity and improving the frequency spectrum efficiency and the energy efficiency of the system.
In order to achieve the above object, the present invention provides a method for user clustering and power allocation of an mimo-NOMA system based on a meta-heuristic algorithm, comprising the steps of:
firstly, constructing a millimeter wave mMIMO-NOMA system and constructing a millimeter wave channel model;
step two, clustering all users by adopting a user clustering algorithm based on cluster head selection to obtain a user clustering result;
step three, mixed pre-coding is carried out aiming at the obtained cluster head channels, and user interference among clusters is eliminated;
and step four, performing power distribution by using a meta-heuristic algorithm based on fusion PSO-SCSO.
As a further improvement of the present invention, in the first step, the millimeter wave mMIMO-NOMA system comprises a digital precoding module, an analog precoding module and G user clusters, and the first step is thatThe cluster contains user->And the user data flow flows into a digital precoding module after being overlapped according to grouping and power distribution, then flows into an analog precoding module and finally is sent to each user.
As a further improvement of the present invention, clustersMiddle->The signals received by the individual users are:
wherein,,representing cluster->Middle user->Is>Representing cluster->Middle user->Is a signal received by the base station;,,representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Is>Representing cluster->Middle user->Is>Is cluster->Middle user->Is a Gaussian noise vector of>;Is an analog precoding matrix, < >>Is the conjugate transpose operation of the matrix,/->Namely +.>Is a conjugate transpose of (2);Representing the +.>Column (S)/(S)>Representing the +.>Column (S)/(S)>Representing cluster->Middle user->Adopts a millimeter wave channel model of a uniform planar array.
As a further improvement of the invention, a user clustering algorithm based on cluster head selection is adopted in the second step to carry out self-adaptive clustering on all users, and the method specifically comprises the following steps:
clustering users according to channel correlation by utilizing the directivity characteristic of millimeter waves, wherein the users in the same cluster use the same analog precoding, namely, the beam gain is obtained from the same beam; the correlation of user channels in the same cluster is high, and the correlation of user channels in different clusters is low; the cluster head user is a strong user in each cluster; the specific algorithm process is as follows:
step1. initializing: initializing user channel gain vectorsWherein->;Is->Channel vector for individual user->,Representing the total number of users; cluster head set->Initially empty; initialization threshold +.>The method comprises the steps of carrying out a first treatment on the surface of the Setting the maximum number of users in each cluster +.>;;
Step2, selecting the channel corresponding to the largest element in the current channel gain vectorAs the current cluster head and removing it from the channel set and channel gain vector;
step3, calculating all remaining user channels in the channel setCorrelation with current cluster headIf and only if the number of users in the cluster does not exceed +.>And->When in use, will->The corresponding user is classified as the corresponding user of the current cluster head>Clusters and removing them from the remaining set of user channels;
step5 repeating Step3 and Step4 until all users have completed clustering, and setting all users to be classified togetherCluster, th->The cluster contains user->If yes, all users are used +.>And (3) representing.
As a further improvement of the present invention, hybrid precoding is used in step three, including analog precoding and digital precoding, wherein the analog precoding is implemented using a phase shifter, only adjusting the phase of the signal; the digital precoding is implemented by a radio frequency chain to adjust both phase and amplitude.
As a further improvement of the invention, in the fourth step, aiming at maximizing the spectral efficiency and the energy efficiency of the system, a meta-heuristic algorithm fused with PSO-SCSO is adopted to solve the user power distribution, and by improving the particle movement mode and fusing with the SCSO algorithm, more accurate results can be obtained after fewer times of iteration.
As a further improvement of the present invention, the meta-heuristic algorithm fusing PSO-SCSO includes:
the PSO-SCSO algorithm is fused, the particle swarm algorithm PSO and the salsa optimization algorithm SCSO are combined, and the development capacity and the global searching capacity of the PSO are improved by utilizing the high-dimensional searching capacity of the SCSO; the fusion PSO-SCSO algorithm updates the particle position in an improved way, and comprises the following algorithm steps:
step1, initializing the size of particle populations, initializing all parameters, and randomly initializing the particle populations;
step2, calculating the fitness value of all particles, and if the fitness value is better than the fitness value of the global optimal position, updating the global optimal position;
step3, updating the positions of all particles by using the following formula;
wherein,,indicate->The individual particles are at->Position vector in the iterative process of times;Indicate->The individual particles are at->Position vector in the iterative process of times;Is a vector introduced;、、Are random numbers between 0 and 1 subject to uniform distribution, ">Is 0 to->Obeying betweenA uniformly distributed random value;、Are all intermediate variables of the formula, and respectively represent main position updating modes of the particles in the early stage and the later stage of movement;Is a global optimal position vector in each iteration process;Is a scalar with an initial value of +.>Gradually reducing in the iterative process;Is a control coefficient;And->Are all acceleration factors;
step4, repeating Step2 and Step3 until the algorithm converges;
step5. Output algorithm updates the location information.
The beneficial effects of the invention are as follows: the invention is suitable for millimeter wave mMIMO-NOMA multi-user systems, adopts a user clustering algorithm based on cluster head selection to cluster users, aims at maximizing the weighted sum of spectrum efficiency and energy efficiency, and adopts an improved meta-heuristic algorithm to carry out power distribution; compared with the traditional meta-heuristic algorithm, the meta-heuristic algorithm shows more accurate search results and faster search speed; which is used for system power allocation, can enable the system to achieve higher spectral and energy efficiency and reduce computational complexity.
Drawings
Fig. 1 is a flow chart of a user clustering and power allocation method for a meta-heuristic based mimo-NOMA system in an embodiment of the present invention.
Fig. 2 is a diagram of a millimeter wave mimo-NOMA system model in an embodiment of the present invention.
Figure 3 is an algorithm flow diagram of a meta-heuristic algorithm incorporating the PSO-SCSO algorithm in an embodiment of the invention.
FIG. 4 is a graph of an algorithm convergence analysis in an embodiment of the invention.
Fig. 5 is a schematic diagram showing a comparison between the spectral efficiency and the signal-to-noise ratio of a system of the power allocation algorithm according to an embodiment of the present invention.
Fig. 6 is a schematic diagram showing a comparison between the system energy efficiency and the signal to noise ratio of the power distribution algorithm according to the embodiment of the present invention.
Fig. 7 is a schematic diagram showing a comparison between the spectral efficiency and the signal-to-noise ratio of a system of a user clustering algorithm according to an embodiment of the present invention.
FIG. 8 is a diagram illustrating a comparison of system energy efficiency and signal-to-noise ratio for a user clustering algorithm according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
As shown in fig. 1, the present invention provides a user clustering and power allocation method for an mimo-NOMA system based on a meta-heuristic algorithm, which mainly includes the following steps:
firstly, constructing a millimeter wave mMIMO-NOMA system and constructing a millimeter wave channel model;
step two, clustering all users by adopting a user clustering algorithm based on cluster head selection to obtain a user clustering result;
step three, mixed pre-coding is carried out aiming at the obtained cluster head channels, and user interference among clusters is eliminated;
and step four, performing power distribution by using a meta-heuristic algorithm based on fusion PSO-SCSO.
The following describes the steps one to four in detail with reference to the accompanying drawings.
In the first step, the first step is to perform,the millimeter wave mMIMO-NOMA system comprises a digital precoding module, an analog precoding module and G user clusters, and is characterized in thatThe cluster contains user->And the user data flow flows into a digital precoding module after being overlapped according to grouping and power distribution, then flows into an analog precoding module and finally is sent to each user.
That is, the first step is specifically: constructing a multi-user millimeter wave mMIMO-NOMA system model shown in figure 2, wherein a BS end is provided withRoot transmitting antenna and->RF chains, simultaneously serving->A random distribution of single antenna users, +.> 。
In order to obtain multiplexing gain sufficiently, the number of RF chains is set equal to the number of beams。
By NOMA technique, users are classified intoCluster, th->Total->The same beam is shared by the individual users.
Order the、Respectively representing an analog precoding matrix and a digital precoding matrix in hybrid precoding, then the cluster +.>Middle->The signals received by the individual users are expressed as: />
Wherein,,representing cluster->Middle user->Is>Representing cluster->Middle user->Is a signal received by the base station;,,representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Is>Representing cluster->Middle user->Is>And->The range of values of ++as described in the cumulative notation>Is cluster->Middle user->Is a Gaussian noise vector of>;Is an analog precoding matrix, < >>Is the conjugate transpose operation of the matrix,/->NamelyIs a conjugate transpose of (2);Representing the +.>Column (S)/(S)>Representing the +.>The number of columns in a row,representing cluster->Middle user->Adopts a millimeter wave channel model of a uniform plane array, and the signal-to-interference-and-noise ratio corresponding to a user is as follows:
wherein:
In the second step, a user clustering algorithm based on cluster head selection is adopted to perform self-adaptive clustering on all users, and a user clustering result is obtained, and the specific method is as follows:
clustering users according to channel correlation by utilizing the directivity characteristic of millimeter waves, wherein the users in the same cluster use the same analog precoding, namely, the beam gain is obtained from the same beam; the correlation of user channels in the same cluster is high, and the correlation of user channels in different clusters is low; the cluster head user is a strong user in each cluster; the specific algorithm process is as follows:
step1. initializing: initializing user channel gain vectorsWherein->;Is->Channel vector for individual user->,Representing the total number of users; cluster head set->Initially empty; initialization threshold +.>The method comprises the steps of carrying out a first treatment on the surface of the Setting the maximum number of users in each cluster +.>;;
Step2, selecting the channel corresponding to the largest element in the current channel gain vectorAs the current cluster head and removing it from the channel set and channel gain vector;
step3, calculating all remaining user channels in the channel setCorrelation with current cluster headIf and only if the number of users in the cluster does not exceed +.>And->When in use, will->The corresponding user is classified as the corresponding user of the current cluster head>Clusters and removing them from the remaining set of user channels; />
Step5 repeating Step3 and Step4 until all users have completed clustering, and setting all users to be classified togetherCluster, th->The cluster contains user->If yes, all users are used +.>And (3) representing.
Step three, hybrid precoding is used, which comprises analog precoding and digital precoding, wherein the analog precoding is realized by using a phase shifter, and only the phase of a signal is adjusted; the digital precoding is implemented by a radio frequency chain to adjust both phase and amplitude.
The third step is as follows: hybrid precoding is performed on the obtained cluster head channels, so that user interference among clusters is eliminated, and a precoding matrix is simulatedOnly the phase of the signal can be adjusted, so analog precoding is designed considering the phase using the conjugate transpose of the channel matrix, while taking into account the accuracy problem of the phase shifter, assuming +.>Bit-accurate phase shifters, the analog precoding matrix can be expressed as:
wherein,,is the cluster head channel of the G user clusters, < >>Representation->Is>Line->Element(s)>Representation->Is>Line->Element(s)>Is an intermediate variable,/->Representing calculating the phase angle of the complex number. After obtaining the analog precoding, obtaining the equivalent channels of all cluster head users as
The digital precoding matrix is:
in the fourth step, aiming at maximizing the spectral efficiency and the energy efficiency of the system, a meta-heuristic algorithm fused with PSO-SCSO is adopted to solve the user power distribution, and a particle motion mode is improved, and the SCSO algorithm is fused, so that a more accurate result can be obtained after fewer iterations.
The meta-heuristic algorithm for fusing PSO-SCSO comprises the following steps:
the PSO-SCSO algorithm is fused, the particle swarm algorithm PSO and the salsa optimization algorithm SCSO are combined, and the development capacity and the global searching capacity of the PSO are improved by utilizing the high-dimensional searching capacity of the SCSO; the fusion PSO-SCSO algorithm updates the particle position in an improved way, and comprises the following algorithm steps:
step1, initializing the size of particle populations, initializing all parameters, and randomly initializing the particle populations;
step2, calculating the fitness value of all particles, and if the fitness value is better than the fitness value of the global optimal position, updating the global optimal position;
step3, updating the positions of all particles by using the following formula;
wherein,,indicate->The individual particles are at->Position vector in the iterative process of times;Indicate->The individual particles are at->Multiple iterationsA position vector in the process;For an introduced vector, it is defined in equation (17);、、Are random numbers between 0 and 1 subject to uniform distribution, ">Is 0 to->Random values subject to uniform distribution;、Are all intermediate variables of the formula, and respectively represent main position updating modes of the particles in the early stage and the later stage of movement;Is a global optimal position vector in each iteration process;Is a scalar with an initial value of +.>Gradually reducing in the iterative process;Is a control coefficient;And->Are acceleration factors, which are defined in equation (19);
step4, repeating Step2 and Step3 until the algorithm converges;
step5. Output algorithm updates the location information.
Specifically, in the fourth step, a meta-heuristic algorithm based on fusion PSO-SCSO is used for power distribution so as to improve the frequency spectrum efficiency and the energy efficiency of the system.
Firstly, determining an optimization target, after completing mixed precoding, firstly sequencing and renumbering users in a cluster according to channel gains, wherein the sequencing result satisfies the following conditions:
the information transmission rate of the mth user in the g cluster is expressed as follows:
the spectral efficiency of the system is expressed as;
the energy efficiency of the system is defined as the number of bits per joule of energy transmitted, expressed as follows:
wherein the method comprises the steps of、、Respectively represents the power of each radio frequency chain, the power of each phase shifter and the power of the base band, +.>Indicating the number of phase shifters. Since the spectrum efficiency and the energy efficiency are key indexes of mobile communication, the invention considers the maximization of the weighted sum of the spectrum efficiency and the energy efficiency as an optimization target to construct the following optimization problems: />
Wherein,,indicating that the transmission power of each user should be a positive number,/->Indicating that the total transmit power of all users is less than the maximum transmit power of the base station +.>,Is the information transmission rate of the mth user in the g cluster, see formula (7), for->Ensuring that the information transmission rate of each user meets the minimum rate requirement +.>。
For easy solution, according to the characteristics of the algorithm, neglectConstraint, converting the constraint maximizing optimization problem into an unconstrained minimizing optimization problem by using a penalty function:
wherein,,representing the spectral efficiency of the system, see equation (8);Representing the energy efficiency of the system, see equation (9); ρ is a penalty factor; the system is divided into G clusters, th->There is +.>Individual user (s)/(S)>Is the transmission power of the mth user in the g-th cluster, and>is the total transmit power constraint of the system;Is the spectral efficiency of the mth user in the g cluster,/->Is the lowest spectral efficiency that meets the individual user requirements.
Aiming at the minimization and optimization problem (11), the traditional optimization algorithm based on classical mathematical theory has a complex calculation process; and the meta-heuristic algorithm obtains a global optimal value through simple calculation by global random search, improves the system performance in order to fully exert the global searching capability of the algorithm, improves the PSO algorithm and fuses the SCSO algorithm.
PSO algorithm:
the PSO algorithm starts from a random initial value, and finally determines a global optimal solution by tracking a local optimal solution in each iteration process. The method is characterized by simple structure and high calculation speed, and is very suitable for solving the multi-objective optimization problem. In the standard PSO algorithm, letAnd->Respectively represent +.>The individual particles are at->Position vector and velocity vector in the next iteration process, then +.>Individual particles from->Iteration number to->The next state update formula is as follows:
wherein,,、is a random number between 0 and 1 subject to uniform distribution, ">Indicate->The individual particles are at->Optimal position of the iteration->Representing a global optimum position->As inertial weight, trust in previous motion state of particles is represented;,the acceleration factors represent the trust of the experience of the particle and the global shared information. Although the PSO algorithm is simple to implement and has high convergence rate, the PSO algorithm also has the defect of being easy to fall into local optimum because the particle motion direction of the PSO algorithm is relatively fixed, so that the PSO algorithm is easy to converge in premature.
SCSO algorithm:
the SCSO algorithm is an optimization algorithm for simulating the survival behavior of the sand cat newly proposed in 2022, has the characteristics of high convergence speed and accurate result, and is better in high-dimensional and multi-objective optimization. Order theRepresenting from->Iterative update to +.>The new position of the population obtained by the iteration is shown in the following formula for updating the particles of the SCSO algorithm.
Wherein,,is->Sub-globally optimal solution,/->Is a populationMiddle Member->The position of the moment->Representation->Local optimal position of each member at moment->Is a random angle for controlling each member of the population to move in different directions in the search space,/or->And->Is a random number between 0 and 1. Other parameters are obtained by the formulas (14 to 16).
Wherein,,、is a random number between 0 and 1, ">Representing the sensitivity range of each sand cat, and generally setting to be 2;、Respectively representing the current iteration number and the maximum iteration number, < ->Is an intermediate variable,/->Is a distance parameter for controlling the behavior of the sand cat.
Fusion PSO-SCSO algorithm
In light of the above description, the PSO algorithm is first improved in order to accelerate the convergence speed of the algorithm and improve the global search capability of the algorithm, and the location update formula is improved as follows:
wherein,,indicate->The individual particles are at->Position vector of the iterative procedure,/->Indicate->The individual particles are at->Position vector in the course of a second iteration, +.>Representing the upper boundary of the position coordinates of all particles, +.>Representing the lower boundary of the position coordinates of all particles, +.>Representing a globally optimal solution vector,>、、are random numbers between 0 and 1, ">The elements are 0 to->Random value between->Represents the step size of the exercise>Control convergence rate, ++>The initial value is->。
In equation (17), the first term replaces the inertia and local optimum factors in the original equation,is a vector pointing to a globally optimal solution, a sine function is used as a coefficient, and the result of the vector is to drive particles to approach or depart from the globally optimal position, wherein the probability ratio of the two is 2:1, such a design accelerates the convergence speed of the algorithm; the second term is that cosine disturbance is added to the current position of the particles, so that the particles start from the current position and followThe machine moves in a range near the optimal position, so that the algorithm has better searching capability; in the third term, the acceleration factor in the original formula +.>The method is replaced by a sine expression, the value of the sine expression is reduced along with the increase of the iteration times, so that the particles are rapidly close to the optimal solution at the initial stage of the iteration, and slowly converged near the global optimal point at the later stage, thereby avoiding the oscillation of the particles near the optimal point and improving the convergence.
Referring again to the attack behavior in the SCSO algorithm, the third term in equation (17) is modified, and the variable coefficients are introduced, and the equation after the second modification is as follows:
wherein,,indicate->The individual particles are at->Position vector in the iterative process of times;Indicate->The individual particles are at->Position vector in the iterative process of times;For a vector to be introduced, it is defined as in equation (17);、、are random numbers between 0 and 1 subject to uniform distribution, ">Is 0 to->Random values subject to uniform distribution;、Are all intermediate variables of the formula, and respectively represent main position updating modes of the particles in the early stage and the later stage of movement;Is a global optimal position vector in each iteration process;Is a scalar with an initial value of +.>Gradually reducing in the iterative process;Is a control coefficient;And->All are acceleration factors, the value and +.>The related steps are as follows:
in the formulae (18) to (19),、、the value of (2) is adjusted according to the actual problem>The calculation of (1) is the same as in the sand cat algorithm. The improved algorithm takes the distance from the global optimum point as a parameter, if +.>,,Plays a main role, and promotes particles to approach to the optimal point; otherwise->,Plays a main role in promoting the searching of particles in a global scope.
The calculation flow of the fusion PSO-SCSO algorithm is shown in figure 3.
The transmitting power of all users is used as the position vector of particles in the algorithm, the algorithm converges after limited iterations, and the output result is the power distribution scheme of the users, so that the frequency spectrum efficiency and the energy efficiency of the system can be maximized.
Under the steps of the embodiment, the beneficial effects of the invention are illustrated by performing simulation experiments on the MATLAB platform.
The table below shows the simulation parameter settings,the system parameters in the table are removed, and the fusion PSO-SCSO algorithm parameters are as follows:,,,the method comprises the steps of carrying out a first treatment on the surface of the Penalty factor->,. Threshold +.>In a random selection +.>Individual user, let->Is 1.25 times the average value of the channel correlation between any two of the users, wherein 1.25 is the empirical value of multiple experiments. />
Fig. 4 is a convergence simulation diagram of different meta-heuristic algorithms, comparing the proposed algorithm with the classical meta-heuristic algorithm, including PSO algorithm, wolf optimization (Grey Wolf Optimizer, GWO) algorithm, whale optimization (whale optimization algorithm, WOA) algorithm, and it can be seen from the diagram that the proposed algorithm achieves convergence within about 10 times, the convergence speed is the fastest and the fitness value is the lowest, and the convergence of the proposed algorithm is verified.
Fig. 5 and fig. 6 are respectively the relations of energy efficiency and spectral efficiency of different algorithms with signal to noise ratio, and it can be seen from fig. 5 that the spectral efficiency of all-digital precoding is the highest, representing the theoretical upper limit, but the cost is high, and it is difficult to apply to practice, so that only reference is made. In the NOMA power allocation scheme, as the signal-to-noise ratio increases, the proposed algorithm is closest to all-digital precoding, and is superior to other schemes. Fig. 6 shows the energy efficiency versus signal-to-noise ratio, and it can be seen from fig. 6 that although the spectral efficiency of all-digital precoding is highest, it is lowest because it requires a large number of radio frequency chains to implement; the NOMA system uses less radio frequency chains and utilizes power domain multiplexing, so that the energy efficiency is greatly improved; and the energy efficiency of the proposed algorithm is better than other algorithms because the proposed algorithm can achieve higher spectral efficiency with the same power consumption.
Fig. 7 and 8 compare the proposed user clustering algorithm with a K-means clustering algorithm, the number of clusters of which is set to a fixed value of 6. As can be seen from fig. 7, as the signal-to-noise ratio increases, the spectral efficiency of the proposed algorithm is significantly better than other algorithms, because the proposed algorithm of the present invention divides the user channels with higher correlation into a cluster, otherwise, they are used as a cluster alone; and the K-means algorithm forcedly divides all users into fixed clusters, so that the situation that the correlation of users in the clusters is low exists, the transmission rate of part of users is low, and the interference among the users in the clusters is not easy to eliminate. While the energy efficiency of the different clustering algorithms is shown in fig. 8, although the actual number of clusters of the proposed algorithm would be higher than the other algorithms, meaning that more RF chains and energy consumption are required, it can be seen from the figure that the energy efficiency is actually slightly higher than the K-means algorithm, so that such a scheme is reasonable.
In summary, the invention is suitable for millimeter wave mMIMO-NOMA multi-user systems, adopts a user clustering algorithm based on cluster head selection to cluster users, aims at maximizing the weighted sum of spectrum efficiency and energy efficiency, and adopts an improved meta-heuristic algorithm to perform power distribution; compared with the traditional meta-heuristic algorithm, the meta-heuristic algorithm shows more accurate search results and faster search speed; which is used for system power allocation, can enable the system to achieve higher spectral and energy efficiency and reduce computational complexity.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the technical solution of the present invention.
Claims (7)
1. The user clustering and power distribution method of the mMIMO-NOMA system based on the meta-heuristic algorithm is characterized by comprising the following steps:
firstly, constructing a millimeter wave mMIMO-NOMA system and constructing a millimeter wave channel model;
step two, clustering all users by adopting a user clustering algorithm based on cluster head selection to obtain a user clustering result;
step three, mixed pre-coding is carried out aiming at the obtained cluster head channels, and user interference among clusters is eliminated;
and step four, performing power distribution by using a meta-heuristic algorithm based on fusion PSO-SCSO.
2. The meta-heuristic based user clustering and power allocation method of a mimo-NOMA system of claim 1, wherein: in the first step, the millimeter wave mimo-NOMA system includes a digital precoding module, an analog precoding module, and G user clusters, the first stepThe cluster contains user->And the user data flow flows into a digital precoding module after being overlapped according to grouping and power distribution, then flows into an analog precoding module and finally is sent to each user.
3. The meta-heuristic based user clustering and power allocation method of a mimo-NOMA system of claim 2, whereinIn that, the clusterMiddle->The signals received by the individual users are:
wherein (1)>Representing cluster->Middle user->Is>Representing cluster->Middle user->Is a signal received by the base station;,,Representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Transmit power of>Representing cluster->Middle user->Is>Representing cluster->Middle user->Is>Is cluster->Middle user->Is a Gaussian noise vector of>;Is an analog pre-coding matrix that is used to determine,is the conjugate transpose operation of the matrix,/->Namely +.>Is a conjugate transpose of (2);Representing the +.>Column (S)/(S)>Representing the +.>Column (S)/(S)>Representing cluster->Middle user->Adopts a uniform planeMillimeter wave channel model of the array.
4. The method for user clustering and power distribution of a mimo-NOMA system based on a meta-heuristic algorithm according to claim 1, wherein in the second step, a user clustering algorithm based on cluster head selection is adopted to perform adaptive clustering on all users, and specifically comprises:
clustering users according to channel correlation by utilizing the directivity characteristic of millimeter waves, wherein the users in the same cluster use the same analog precoding, namely, the beam gain is obtained from the same beam; the correlation of user channels in the same cluster is high, and the correlation of user channels in different clusters is low; the cluster head user is a strong user in each cluster; the specific algorithm process is as follows: step1. initializing: initializing user channel gain vectorsWherein->,Is->The channel vector of the individual user(s),,representing the total number of users; cluster head set->Initially empty; initialization threshold +.>The method comprises the steps of carrying out a first treatment on the surface of the Setting the maximum number of users in each cluster +.>;The method comprises the steps of carrying out a first treatment on the surface of the Step2, selecting the channel corresponding to the largest element in the current channel gain vector>As the current cluster head and removing it from the channel set and channel gain vector; />
Step3, calculating all remaining user channels in the channel setCorrelation with current cluster headIf and only if the number of users in the cluster does not exceed +.>And->When in use, will->The corresponding user is classified as the corresponding user of the current cluster head>Clusters and removing them from the remaining set of user channels; step4.;
5. The meta-heuristic based user clustering and power allocation method of a mimo-NOMA system of claim 1, wherein: step three, hybrid precoding is used, which comprises analog precoding and digital precoding, wherein the analog precoding is realized by using a phase shifter, and only the phase of a signal is adjusted; the digital precoding is implemented by a radio frequency chain to adjust both phase and amplitude.
6. The meta-heuristic based user clustering and power allocation method of a mimo-NOMA system of claim 1, wherein: in the fourth step, aiming at maximizing the spectral efficiency and the energy efficiency of the system, a meta-heuristic algorithm fused with PSO-SCSO is adopted to solve the user power distribution, and a particle motion mode is improved, and the SCSO algorithm is fused, so that a more accurate result can be obtained after fewer iterations.
7. The meta-heuristic method for user clustering and power allocation of a mimo-NOMA system based on the meta-heuristic algorithm of claim 6 wherein the meta-heuristic algorithm fusing PSO-SCSO comprises:
the PSO-SCSO algorithm is fused, the particle swarm algorithm PSO and the salsa optimization algorithm SCSO are combined, and the development capacity and the global searching capacity of the PSO are improved by utilizing the high-dimensional searching capacity of the SCSO; the fusion PSO-SCSO algorithm updates the particle position in an improved way, and comprises the following algorithm steps: step1, initializing the size of particle populations, initializing all parameters, and randomly initializing the particle populations;
step2, calculating the fitness value of all particles, and if the fitness value is better than the fitness value of the global optimal position, updating the global optimal position;
step3, updating the positions of all particles by using the following formula;
wherein (1)>Indicate->The individual particles are at->Position vector in the iterative process of times;Indicate->The individual particles are at->Position vector in the iterative process of times;Is a vector introduced;、、Are random numbers between 0 and 1 subject to uniform distribution, ">From 0 to 0Random values subject to uniform distribution;、Are all intermediate variables of the formula, and respectively represent main position updating modes of the particles in the early stage and the later stage of movement;Is a global optimal position vector in each iteration process;Is a scalar with an initial value of +.>Gradually reducing in the iterative process;Is a control coefficient;And->Are all acceleration factors; />
Step4, repeating Step2 and Step3 until the algorithm converges;
step5. Output algorithm updates the location information.
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